CONTACT FORCE: when objects are physically touching eg. reaction force, friction, tension.
NON-CONTACT FORCE: without objects physically touching eg magnetism, electrostatic force and gravity a VECTOR is a quantity with MAGNITUDE & DIRECTION. a SCALAR is a quantity with MAGNITUDE only.
here, gravitational field strength is 9.8N/g. that means every 1kg has a weight of 100.
WORK DONE just means energy transferred by a force. this means that if you hold an object or lift at A CONSTANT
speed, you must be pushing upwards with a force that's the same size as its weight!
any object that deforms ELASTICALLY (returns to its original shape) obeys HOOKE'S LAW
force is directly proportional to extension.
gradient = spring
constant.
PRACTICAL:
add masses onto spring to change force.
measure extension with ruler at each weight, plot f against e.
gradient of graph = spring constant.
avoid systematic error by lining up 0cm with bottom of spring.
avoid parallax error by getting on eye level when measuring
the GRADIENT of a DISTANCE/DISPLACEMENT-
TIME graph gives you
the SPEED/VELOCITY.
the gradient of a SPEED/VELOCITY - TIME graph is ACCELERATION
while the area under the graph gives you DISPLACEMENT.
NEWTON'S 1st LAW: if no resultant force acts on an object, its motion will be constant (velocity will not change).
NEWTON'S 2nd LAW: F= ma
NEWTON'S 3rd LAW: for every action (force), there is an equal and apposite reaction (force).
F= ma PRACTICAL:
accelerate the trolley on track with slotted mass on string over pulley.
use lightgate to measure acceleration.
change force by removing masses and placing on trolley to keep total mass the same.
use f= ma.
STOPPING DISTANCE = THINKING + BRAKING.
THINKING DISTANCE is affected by;
speed (proportional)
distractions
alcohol
alcohol
tiredness
STOPPING DISTANCE
is affected by:
speed
condition of brakes, tires and road
weather conditions
momentum= mass x velocity
in any collision, TOTAL MOMENTUM iS ALWAYS CONSERVED.
TYPES:
• rebound
• coupling
• recoil
WAVES
transfer ENERGY without transferring MATTER
LONGITUDINAL WAVES: direction of oscillation is PARALLEL with the direction of energy transfer (eg sound, seismic). consists of COMPRESSIONS AND REFRACTIONS
TRANSVERSE WAVES: the direction of oscillation is PERPENDICULAR with the direction of energy transfer (eg water, light, EM).
WAVES PRACTICALS
SOUND
someone makes a noise whilst standing within proximity of a wall. another person starts a stopwatch when they hear it, stopping it when the sound echoes and they hear it again.
LIQUID
ripple tank, light above, paper below. motor-powered dipper on the surface.
take photos/videos to measure frequency and wavelength.
change motor speed and repeat.
SOLID
attatch string to a vibrator /energy generator, pulling it tout with a ramp and adding masses to the end.
measure wavelength with a metre ruler.
frequency changed by adjusting generator, adjust tension by changing masses (depends what you’re investigating)
put into equation.
all EM waves are EMITTED and ABSORBED by ELECTRONS
except for gamma. they’re emitted by nuclei
if the ENERGY of the wave is high enough it can cause an electron to leave its atom leaving an ion. UV and GAMMA are worst
RADIO WAVES
phone, wifi
MICRO WAVES
cooking, absorbed by H2O
INFARED
cooking, absorbed by surface
VISIBLE LIGHT
vision
ULTRAVIOLET
tanning, can cause cancer
X RAYS
medical scans, dangerous
GAMMA RAYS
sterilisation, medicine, dangerous
PRACTICAL:
show that MATTE BLACK is the best emitter and absorber of IR: use LESLIE CUBE with THERMOMETER or tubes wrapped in different materials under the source .eg. IR lamp. SHINY materials are the WORST emitters and absorbers
When waves enter a new MEDIUM (material) their SPEED changes, as does their ANGLE.
if SPEED decreases, WAVELENGTH does, whilst FREQUENCY remains constant. we only need to draw the RAYS, not the WAVEFRONTS
if the wave slows down, it bends towards the NORMAL (eg going from air into another material)
the angle of REFRACTION is SMALLER than the angle of INCEDENCE
when the light exits, it speeds up again and bends AWAY from the NORMAL
PERMANENT magnets always produce a magnetic field whereas INDUCED magnets become magnetised when in another magnetic field.
mini compasses or iron filings can be put in a magnetic field to visualise it. we always draw the field lines going from North to South pole.
IRON, COBALT and NICKEL are magnetic (can become induced magnets) and so are attracted
to permanent magnets. Other metals aren't.
a CURRENT CARRYING wire in a MAGNETIC FIELD will experience a force (as it produces its own magnetic field that will interact with the other).
PRACTICAL
FINDING MAGNETIC FLUX DENSITY
place magnet on balance.
tare balance, measure mass when known current flowing.
convert to newtons.
measure lenath of wire in field.
rearrange f=BIL to calculate B.
right hand rule= current in wire.
left hand rule = direction of force.
motors use the motor effect, both sides of a coil experience a force in opposite directions, and it turns.
TO INCREASE SPEED (motor effect):
•add more turns to the coil
• increase voltage/current
• use a stronger magnet
a SPLIT RING COMMUNICATOR is used to ensure that the current is reversed every half turn to keep the coil spinning
LOUDSPEAKERS use the motor effect:
a current is sent from the source, causing the COIL and SPEAKER CONE to vibrate, sending sound waves